The invention relates to a process for the conversion of solid, mostly dehydrated waste substances into glass, wherein the waste substances are mixed with one or several additives to form a batch to be melted. A major portion of the batch is melted into a glass melt by supplying heat and a minor portion is exhausted from the melting batch as an exhaust gas. Solid vitreous bodies are formed from the glass melt by means of casting and cooling. Furthermore, the invention relates to an apparatus for the working of this process.
It has long been known, to convert toxic and radioactive waste substances in the form of slurries or suspensions into glass by means of melting after mixing it with additives to form a batch. The formerly loose waste substances are now tightly incorporated in the glass. Glass possesses the advantageous property that it is difficult to leach out, thus permitting the release of heavy metal and other substances contained in the glass only to such a small extent that the storage or the use of bodies made of such glass does not cause any problems. Such processes are disclosed, for example, in U.S. Pat. Nos. 4,139,360 and 4,666,490. Furthermore, DE-A 3700382 (Pieper) specifies the incorporation of heavy metals in glass and calcium sulfate. They are integrated into the glass melt only to a very small extent during the melting process even if the chloride and sulphur capacity of the glass melt is completely saturated, which is due to the large amount of these substances present. Hence, large amounts of exhaust gas containing gases of chlorides and sulfate, especially Cl, HCl, SO.sub.2, and SO, are a disadvantageous result. In contrast, heavy metals are sufficiently absorbed by the glass, but heavy metals and alkali still escape from the glass melt by means of vaporization. The most aggravating disadvantage of the known process, especially with regard to its environmental effects, is the formation or possible formation of dioxin and/or furan when the batch is heated during the melting process. This occurs when the waste substances to be converted still contain organic components, from which these harmful substances are formed under temperatures occurring during the melting of the batch.
Copending U.S. application Ser. No. 07/370,595, incorporated herein by reference, addresses the foregoing disadvantages and provides a process which is less harmful to the environment and excludes especially the emission of dioxin and/or furan even if heterogeneous, organic components as well as heavy metal are employed. According to the process, the waste substance is incineration ash, and hot exhaust gas is withdrawn under exclusion of surrounding air and reintroduced into the batch to be melted where it is cooled down to 20.degree. to 50.degree. C. Condensation products resulting from the cooling process are melted with the batch, and the cold exhaust gas emerging from the batch to be melted is purified.
The process permits the conversion of a so far very problematic waste substance, i.e. incineration ash, into glass in an ecologically beneficial way despite the fact that such ash products are heterogeneous and consist of high and unstable percentages especially of carbon, mercury, lead, tin, zinc, calcium, chlorides, and halides. A major portion of these harmful substances is directly integrated into the glass melt, hence, they are tightly incorporated. Harmful substances escaping as gases are mostly condensed by cooling within the batch to be molten and then reintroduced into the melting mass. The remaining, relatively small amount of cold exhaust gases are neutralized in a subsequent purification process.
For additional details, the reader is referred to said application.